The present invention relates to circuitry for the generation of electrical impulses and, more specifically to a symmetrically charged pulse-forming circuit.
Many circuits have been designed to generate a high voltage pulse and apply it to an electronic device. One such circuit includes two pulse-forming networks, each formed by series inductors and shunt capacitors, with the load positioned between the networks. This type of circuit has come to be known as a Blumlein pulse circuit and is of the general type shown in FIG. 3 of U.S. Pat. No. 2,496,979 to A. D. Blumlein. A charging inductor parallels the load, which is shown as a magnetron, and a charging circuit is connected to one pulse-forming network. The loads used with such circuits have characteristics of a diode in that they have a cathode and an anode. When forward biased (or in their "operating" state) they have a low impedance, and when reversed biased (or in their "non-operating state"), they exhibit a high impedance. The charging inductor has an impedance which is low compared with that of the load when in its "non-operating" state but high compared with that of the load in its "operating" state. Thus, the pulse-forming network not directly connected to the charging circuit must be energized through the charging inductor, which subjects the load to a voltage drop causing a "pre-pulse" to be applied to the load. As used herein, the term "pre-pulse" simply means that a voltage drop appears across the load during charging of one of the pulse-forming networks. After the capacitors of the pulse-forming networks making up the Blumlein pulse circuit are charged, a switch at the distal end of one of the pulse-forming networks, is closed. As will be discussed more fully hereinafter, this closing results in the energy in the one pulse-forming network being redistributed so that the polarity of the voltage across the capacitors in the first network is reversed and the reversed voltage is applied across the load in series with the voltage across the capacitors in the second network.
While some electronic devices, such as a magnetron, can tolerate the existence of a pre-pulse during charging of the networks, other electronic devices cannot. One such device is an electron beam laser. This laser has a cathode which is sensitive to the voltage applied so that voltage deviations with respect to time will prevent proper ignition and/or will disturb laser kinetics.
Another pulse-forming network arrangement of the Blumlein type is disclosed in U.S. Pat. No. 3,189,837. The circuit shown in this patent also discloses the use of a single charging circuit, but here each pulse-forming network is charged using a center-tapped charging inductor so that no pre-pulse appears across the load during charging of the capacitors in the pulse-forming networks.